Mentioning no names, it is interesting I had one conversation about what I can only call aspects of paranoia and how to deal with them, and the next call was exactly the same almost word for word but from a different viewpoint and quite a bit of insight into what may be going on.
Now that has told me that the standard symptoms of paranoia of nasty voices and the idea your mind is being probed are clearly something which needs to be treated, and exploit a physical weakness in the brain, and as a result allows in all sorts from wherever it's coming from. As we all have different dreams each night, let alone different from other people, which are usually generated internally, then surely if people who hear voices were accessing the same sort of mechanism then they'd get totally different things but they don't. Having both worked with and known many typical paranoids the similarity in what they are hearing is so close you'd assume it was all coming from the same place, although we really don't know where. But if someone has a problem with the brain which normally blocks out such communications, why would it all be negative? The answer of course is that it isn't, but if you hear positive and helpful voices you are considered a channeler and great teacher, and would very rarely complain or be diagnosed with mental illness as you are being given genuine information with practical benefits.
So the first likely conclusion is that due to physical weaknesses in the brain these communications enter the awareness, but depending if positive or negative are either diagnosed with paranoia or seen as a great mind. On a personal note I have found very little quality in such teachings myself, most seems like recycled commonsense or judgment which is almost as negative as the other type but dressed up as beneficial. When I've looked further into it it usually tells people they are doing things wrong and if they think right they'll get better results in life. Then they almost kill themselves trying to change, get no better results, and then feel even worse.
So basically you start with the similarities which imply the voices people hear are more likely to have an external than internal source, although we can't yet locate it. Then the nature is either destructive or apparently positive, but maybe similar material posing in different ways. I expect a little of it would be genuinely helpful but having teased through a few decades of channeled material most is trite truism and of little practical use although there is probably a small fraction which is the real thing, but anyone connecting to something positive wouldn't normally be considered mentally ill although still receiving voices but not disturbed by it. But it's all very real one way or another.